The power control technique for inverters is known in the art. For instance U.S. Pat. No. 6,791,239 discloses a technique to overcome problems encountered in a conventional inverter circuit. The conventional inverter circuit usually includes a pulse-width modulation (PWM) control unit, driving unit, and voltage boosting unit to drive individual charge lamp (CCFL or EEFL). With the size of display panels becomes bigger, the number of the discharge lamps required also increases. And the needed power also has to increase. To configure the PWM control unit, driving unit and voltage boosting unit according to the number of the discharge lamps not only has to increase the size of the circuit board, circuit configuration also is more difficult to do. Moreover, the discharge lamps tend to have luminance and electric field interference and result in non-uniform brightness. The patent mentioned above aims to provide an improvement that allows a single PWM control unit to synchronously output driving signals of the same phase and frequency according to the driving units and voltage boosting units required to drive the same number of discharge lamps at the rear end. Thereby each driving unit, voltage boosting unit and discharge lamp can be driven synchronously to achieve a uniform brightness.
INFORMATION DISPLAY October 2005 Vol. 21, No. 10, page 28 discloses a backlight technique “Dynamic-Scanning Backlighting Makes LCD TV Come Alive”. Due to the display panel of the LCD transforms a liquid cell to a pixel in different electric fields, a transformation time difference occurs between a preceding image and a following image. This is also called rise-time or fall-time. The picture on the general LCD panel is updated at a frequency of 60 Hz, namely the picture has to be changed 60 times per second. Whether the preceding picture is altered on not, it has to be re-displayed at such a frequency. Hence each picture lasts 1/60=16.67 ms. If the rise-time is greater than this value, a blurred image occurs while the picture changes cyclically. To overcome this problem, the present design of the display panel focuses on reducing the rise-time to enhance the image quality of the display panel. But merely reducing the rise-time is not enough. As the actual transformation speed of gray scale is faster than the rise-time, hence if the light source is eliminated during the transformation of the gray scale, the rise-time can be confined only to transformation of black and white color scale. This can improve the picture quality of the display panel. The backlighting technique set forth above proposes a light source scanning technique which provides light only when the image is displayed, and the power of the backlight is turned off during the pixel rise-time so that not light is emitted. But in that technique the inverter of the backlight source has to be turned off at every duty cycle to stop delivering power. This is prone to damage the inverter, especially for the piezoelectric inverter driven by a high resonant frequency. The duty cycle is based on μs. If the width of controlling OFF cycle is too short, an instantaneous energy is generated according to the oscillation principle of the piezoelectric inverter. And an actual OFF condition cannot be achieved. On the other hand, if the width of controlling OFF cycle is too long, the piezoelectric inverter has to repeat oscillation from zero potential to a high potential to activate. The constant oscillation at high amplitude tends to damage the piezoelectric inverter. Hence while technique mentioned above could be adopted for a winding inverter to achieve a satisfactory result, it cannot be used effectively on the piezoelectric inverter.